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youtube.com/… (sorry, I couldn't resist :D I think it's pretty relevant though, as SO.YO.NA was the Kansai-ben version of DA.YO.NE, that was also localized into various other dialects.)
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cypherJul 3 '12 at 3:20

(typo: SO.YO.NA -> SO.YA.NA) just thought I'd add: there's not really much difference between そやな and せやな in meaning, but there's an image of せやな tending to be used more by people over 40 and そやな used by comparatively younger people according to this article.
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cypherJul 3 '12 at 4:46

Yes... my friend also says she thinks せや~ is more used by older people and そや~ by younger people. I've always thought せや~ is used more in Osaka and そや~ is more used in Kyoto.
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user1016Jul 3 '12 at 5:11

I also say
●せやで(or そうやで) for そうなのよ/そうなんだよ(Compared with せやねん, I think せやねん is more subjective and せやで sounds a bit more objective)
●せやて/せやって(or そうやて・そうやって) for そうだって/そうだってば/Right,(trust me, that's the truth...)/(sounds like you're trying to persuade or repeating what you've just said)
●せやかて(or そやかて)/せやけど(orそやけど) for そうだけど/それでも/そうだとしても/You're right, but.../You may be right, but.../You say so, but...
●せやし(or そやし) for だから/そうだから/so.../therefore...
●せやった(or そやった) for そうだった(the past tense of そうだ)

You have already received several answers. Rather than repeat them, let me give you the resources so that you can answer this and similar questions on your own. Look for a book titled 『大阪ことば辞典』 by 牧村史陽 (Makimura Shiyō) and published by Kōdansha, 1984. The ISBN is 4-06-158658-0. Below are a few short excerpts.